Abstract
The three-dimensional micro-structure of physical surfaces produces frictional forces that provide sensory cues about properties of felt surfaces such as roughness. This tactile information activates somatosensory cortices, and frontal and temporal brain regions. Recent advances in haptic-feedback technologies allow the simulation of surface micro-structures via electro-static friction to produce touch sensations on otherwise flat screens. These sensations may benefit those with visual impairment or blindness. The primary aim of the current study was to test blind and sighted participants’ perceptual sensitivity to simulated tactile gratings. A secondary aim was to explore which brain regions were involved in simulated touch to further understand the somatosensory brain network for touch. We used a haptic-feedback touchscreen which simulated tactile gratings using digitally manipulated electro-static friction. In Experiment 1, we compared blind and sighted participants’ ability to detect the gratings by touch alone as a function of their spatial frequency (bar width) and intensity. Both blind and sighted participants showed high sensitivity to detect simulated tactile gratings, and their tactile sensitivity functions showed both linear and quadratic dependency on spatial frequency. In Experiment 2, using functional magnetic resonance imaging, we conducted a preliminary investigation to explore whether brain activation to physical vibrations correlated with blindfolded (but sighted) participants’ performance with simulated tactile gratings outside the scanner. At the neural level, blindfolded (but sighted) participants’ detection performance correlated with brain activation in bi-lateral supplementary motor cortex, left frontal cortex and right occipital cortex. Taken together with previous studies, these results suggest that there are similar perceptual and neural mechanisms for real and simulated touch sensations.
Highlights
The sense of touch is an integral part of our lives
The haptic-feedback touchscreen we used in the present study is not MR-compatible. To overcome this limitation for our preliminary functional magnetic resonance imaging (fMRI) experiment, we focused on correlating brain activation to physical vibrations, as measured by the blood oxygenation-level dependent (BOLD) response, with tactile detection performance, as measured by observers’ tactile sensitivity functions to electrostatic induced frictional forces outside the scanner
In Experiment 2 using fMRI, we investigated whether brain activation in the somatosensory network to physical vibrations correlated with sighted observers’ tactile sensitivity functions for simulated tactile gratings
Summary
The sense of touch is an integral part of our lives. For those with visual impairments or blindness, touch is a critical substitute, allowing for important tasks such as reading Braille. Recent technological advances have made it possible to simulate this micro-structure on an otherwise flat touchscreen by digitally manipulating electric current or ultrasound to produce frictional forces on the touchscreen (Bau et al, 2010; Meyer et al, 2013; Mullenbach et al, 2013; Vardar et al, 2016, 2017; Vezzoli et al, 2016; see Culbertson et al, 2018, for a review) These forces impede the movement of the finger, giving rise to simulated texture patterns. In a preliminary functional magnetic resonance imaging (fMRI) study, we used a correlational approach to explore in sighted observers possible brain regions that may be involved in processing simulated tactile gratings
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